Not too far off it myself, but I save 75%+ of my post-tax income. Note that I do not deprive myself of luxuries, I am merely skilled at delayed gratification and grew up very financially unstable. I have a lovely 2017 car with < 1600 miles on it (purchased brand new), but I take the bus to work, for example. I do keep my finances very close to my chest for fear of judgement from others - I did not reveal the $ amount to my fiance-to-be until we had been dating for 4 years.

My timeline is 5-10 years to be safe (age ~40). However, I get satisfaction out of creating and delivering software, beyond collecting a paycheck and don't have any intention to stop working - just not as a wage slave once I've reached my number.

I am hard-pressed to think of mistakes that software engineers would make that people in other professions don't make - there are the usual things like buying too much house, too much car or letting someone else spend your money. Perhaps the only unique-ish mistake would be to assume the large salaries will last forever and not save for contingencies. My impression of people in finance is that they know they're worked like dogs, so they are trying to get out as soon as possible. Tech is so cushy that people can get lulled into forgetting that there's more to life than foosball and free lunch.